You can't. (OH YES YOU CAN! See post #8). What you CAN do is delete your post - and that will delete the entire forum (I believe), if yours is the first post. NO, THAT FUNCTIONALITY CHANGED! YOUR COMMENT GETS REPLACED BY [Comment Deleted].
A useful facility - in the absence of being able to edit the title (other than by completely deleting the discussion and starting over) - would be the ability to add a subtitle. In the case of this discussion:
TITLE: why do patzers delude themselves that non-patzers are cheats?
SUBTITLE: whiner-patzers
I'm thinking that a subtitle is something you might add later on in the discussion to emphasise the essence. (And it would be neat to be able to edit it, of course!)
Ideally, the sub-title would act as a searchable keyword - but not be part of the URL to the topic (http://www.chess.com/forum/view/community/forum-feature-i-would-like)
How can I correct the title of my previously posted topic, if I found out the mistake in it?